The present invention relates to the general field of cooling blades in turbomachine gas turbines. More particularly it seeks to improve the cooling of a blade provided with a cooling cavity having a high aspect ratio.
It is known to provide the moving blades of a turbomachine gas turbine, such as the high and low pressure turbines, with internal cooling circuits enabling them to withstand without damage the very high temperatures to which they are subjected while the turbomachine is in operation. For example, in a high pressure turbine, the temperature of the gas coming from the combustion chamber reaches values well above those that can be withstood without damage by the moving blades of the turbine, which has the consequence of limiting their lifetime.
By means of internal cooling circuits, air which is generally injected into the blade by its root, travels along the blade, following a path formed by cavities made inside the blade, prior to being ejected through orifices opening out into the surface of the blade.
Nevertheless, those cooling circuits are unsuitable for blades that are “long and thin”, i.e. blades presenting a thickness (maximum distance between the pressure side face and suction side face of the blade) that is considerably smaller than their radial height (distance between the root and the tip of the blade).
One of the constraints associated with such blades is the small air flow rate available for cooling them. This means that it is necessary to adopt a cooling cavity that is fine, i.e. that has a high aspect ratio, in order to increase the internal air flow speed, and thus increase heat exchange coefficients. Since such a modification is not sufficient for cooling the blade, it is also necessary to disturb the internal flow, e.g. by means of spike or bridge type flow disturbers.
Nevertheless, the use of conventional disturbers is made impossible by the fineness of the cooling cavity in such blades. In particular, the presence of spikes in the cooling cavity impedes the flow of air passing therethrough excessively and leads to reduced mechanical strength which is a source of crack starters. Bridges also raise problems of fabrication when casting blades.